# include <iostream>

using namespace std;
void test01(){
    string str="hello world";
    for (int i = 0; i <str.size() ; ++i) {
        cout<<str[i]<<" ";
    }
    cout<<endl;
    for (int i = 0; i <str.size() ; ++i) {
        cout<<str.at(i)<<" ";

    }
    cout<<endl;
    str[0]='x';
    str.at(1)='x';
    cout<<str<<endl;
}
int main() {
    test01();
    system("pause");
    return 0;
}
